For the seventh time, we put the year's hottest performance cars to the ultimate test.

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Here is cruel proof of what a track can do to an otherwise estimable sports sedan. Fresh out of the box, the new S6 bested the Mercedes-Benz E63 AMG and the BMW M5 in a comparison test. Then we sent this example, as white as coconut meat and freshly shod with new tires, out on VIR's evil asphalt. The result was a wince-inducing horror show of understeer and lap times that didn't come close to the M5's.

Because all-wheel-drivers tend to understeer, a certain iron fist is often required to hustle them around a track. It's best to storm up to a corner, hit the brakes hard, jump off the brakes abruptly to tease the car into rotating, and then stomp on the gas in the hope it'll provoke the rear axle to do something useful. But the Audi, even fitted with a torque-vectoring rear differential, proved immune to our cattle prodding. We also tried to be gentle, but the S6 just wouldn't bite. It took achingly long to get through the slower turns as the front tires squealed their arias of woe. And at 4369 pounds, the S6 could only make it to 136 mph on the straight.

Once straightened out, the twin-turbo V-8 quickly boiled up its steam and the S6 left a thrilling, big-bore sound in its wake. The dual-clutch transmission makes up in lightning shifts and downshifting throttle blips what the rest of the chassis lacks in track aptitude. In our estimation, however, the Audi leaves the event as it entered—as the market's best big, fast, luxury car—even if it's a machine that can't be what it wasn't intended to be.

BMW M5 • 3:05.2

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If there is a hero in the M5's 3:05.2 lap, it's the twin-turbo 4.4-liter V-8. It's a war horse that pulls the wagon and refuses to yield under fire.

But braking, as most racers know, is often what puts a car on pole. The M5's brake pedal lacks tactility, so we struggled to find the ideal braking points. One lap would feel great. Then, on the next, we would be braking way too late, and then on the third lap, the anchors somehow revived again. The brakes never failed, but their inconsistent performance shook our confidence.

Whether the M5 is braking or turning, this car weighs 4425 pounds. There is only so much you can ask of its Michelin Pilot Super Sports—maybe a few laps of good grip, but then the rubber greases up and the understeer sets in fully.
The thick-rimmed steering wheel is a track rat's dream. The large diameter and the squishy rim reduce grip fatigue. However, the good marks stop there. Little is communicated up the column from the contact patches and the weighting seems pointlessly hefty, especially in the sportiest of the three settings.

Not one single sector highlighted any particular M5 strength. All its skills were just so-so, both by the clock and by the seat of our pants. The engine is ultimately what drives the lap time down below the BMW M3's, and to just 0.3 second slower than the Mercedes-Benz CLS63 AMG. Interestingly enough, the Benz and the M5 carry nearly identical pounds per horsepower.

BMW M6 • 3:04.7

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The M division's big twins couldn't be more similar. There were moments when we struggled to recall which car we had just vacated. "Was it the M5 or the M6?" We'll make sure to remember that the M6 is the quickest BMW in Lightning Lap history, within a mere 0.5 second of the Cadillac CTS-V coupe.

As with the M5, understeer and a general lack of feedback from the braking and steering systems soured our confidence and the M6's lap time suffered. The BMW's back end moves around under braking, and, even with the M6's $10,000 carbon-ceramic brakes ($8700 for the hardware plus $1300 for the required 20-inch wheels), slowing down two tons of German sports coupe requires faith in the engineering.

Because it's so big and heavy, the M6, which tops out at 142 mph, feels every bit as fast as the 158-mph Ferrari while hauling the mail down the straightaway. However, the bulkiness sensed from behind the wheel, thanks to the high, broad dash and long hood, also makes it difficult to place the M6 exactly on the apex.

As in the M5, the engine is the real story here. The car will get away from you if you don't keep close tabs on the speed, as one adventurous and, fortunately, damage-free 115-mph off-track event taught us. With a ­little attention to the brakes and steering systems, BMW's M GmbH could transform a fantastic touring car into a truly satisfying track animal.

Audi RS5 • 3:04.3

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Of all the sub-3:10 cars we've subjected to VIR, nothing has felt as slow as the RS5. Maybe it's the high-revving and peaky 4.2-liter V-8, which doesn't press you into your seat like the twin-turbo V-8 in the BMW M5 and M6.

Not that a 3:04.3 lap is slow by any stretch. But Turn One exposes the RS5's major weakness: understeer. With 57.7 percent of the RS5's 4053 pounds on the front axle, we could see it coming.

The RS5 doesn't shine until the second half of the track, after the back straight. It matches both Camaros and the Boxster S in sector three, through the downhill corkscrew; in sector four, though, where the flowing uphill combinations seem purpose-built for this car, the RS5 actually proved slower than the Chevy V-8s. Even so, it felt better on these fast, open corners than it did in sector three, where the tight radii summon Mr. Plow. The RS5 becomes fun on the wider turns, where managing speed with full- or part-throttle loads the rear and alleviates some stress on the front tires. It allows the RS5's torque-vectoring differential to do its thing, helping the car rotate. Carrying a lot of speed, at least 65 mph, through the last corner aids a major Audi-on-Audi victory by crossing the line 0.3 second before the mid-engined R8 we tested in 2007.

Porsche Boxster S • 3:04.2

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Porsche has completely transformed the on-track demeanor of its new 911, but the latest Boxster's lap times barely budge this year despite being on a new ­platform. But since we're comparing this stand­ard Boxster S to the lowered, raw, lightweight, and sublime Boxster Spyder we had two years ago, this is actually a huge accomplishment. The Boxster S is only 0.4-second slower than the more radical Spyder over the 4.1-mile lap.

Down five horses to the Spyder and weighing 154 pounds more, the S is such a close match to the old Spyder because, despite the S's liveable ride, it is nearly as sharp. The Boxster's platform sports a ­significantly wider front track and a slightly wider rear track. The front grip is tenacious. Shockingly, for a car with stability control that can be fully disabled, and in a country where drivers can't discern between the brake and the accelerator, the handling ­balance is tilted slightly toward oversteer. Like a racer, the Boxster's rear end is especially susceptible to load transfer. Brake too deeply, and the rear tires slide wide. Lift gently to reduce understeer, and the tail swings. Keeping oversteer at bay requires a consistent and gentle throttle, especially when the tires are hot and greasy. At least two days of on-track driving school should be the prerequisite to disabling the stability control.

Typical of a Porsche, the brake strength and pedal feel are the envy of the industry. On corner exit, the speed isn't limited by grip, but by the 3.4-liter flat-six's 315 horsepower. So the 2013 Boxster S is nearly as quick as the 2012 Boxster Spyder. Naturally, we can't wait for the new Boxster Spyder.

Ford Shelby GT500 • 3:00.6

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At 662 horsepower, the Ford Mustang Shelby GT500 is the most powerful car we've tested at VIR. So why couldn't it put down a sub-three-minute lap? Why didn't it beat the heavier and less potent Camaro ZL1? It comes down to two related reasons: balance and traction.

Yes, the GT500 is lighter than the ZL1, but that's not the full story. Look at where it carries its weight—the GT500 puts 56.6 percent of its 3896 pounds over its front wheels. The ZL1 achieves a better balance with 52.9 percent of its mass resting up front. Nose-heavy, powerful, and rear-drive is a combination that makes putting power to the ground difficult. Just ask anyone driving a two-wheel-drive pickup in the snow.

As a result, with just 43.4 percent of its mass over its powered rear wheels, the GT500 couldn't accelerate as hard out of corners as the ZL1, couldn't get its full power down, couldn't turn its impressive horsepower into miles per hour. Still, the Shelby's turn-in grip is strong. In sector one, the GT500 matches the ZL1's peak roadholding. But at the corner's exit, the GT500 is 4.6 mph slower. Balance is part of the problem, and the GT500 also has narrower wheels and tires than the ZL1. On the track, the rear contact patches feel dime-sized.

Quick transitions upset the GT500 more than the ZL1 and cost time in the uphill esses. Good brakes are a plus, but the GT500 is a car that is not comfortable ­cornering at the limit. VIR proves, once again, that handling can trump a superior power-to-weight ratio.

Porsche 911 Carrera S • 2:58.9

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It didn't take long to dial in the new 911's lap time. Unlike its immediate predecessor, the new 911—or 991 in Porsche Sprache—is comfortable at the limit. And, once you find that limit, it's easy to stay there. Much of the credit has to go to the 991's four-inch-longer wheelbase and its widened front track.

The 911 is a car taken off its toes and put on its feet. Porsche smoothed out the 911's dartiness and jumpiness, and directional changes are less frantic than before, making it a more settled, more capable track car.

Comparing the 400-hp Carrera S with its predecessors is telling. Through the uphill esses, the 991 is fractionally quicker than the previous-gen, 530-hp 911 Turbo S despite entering the sector at a speed that was 6.5 mph slower than the Turbo's. Stability pays a big dividend in this section, and the new 911's poise makes it easier to put the power down sooner out of a corner. Witness how the 991 exited the sector-two esses 5.3 mph faster than the Turbo S.

Pointed downhill in sector three, the 991 proved to be a tenth of a second quicker than the race car–like 911 GT3 RS. Here again, improved stability and the greater confidence it bestows allow for higher speeds. The rear end remains planted and the grip is easy to manage. Beating out the track-hungry GT3 RS in this section is all the more shocking considering the Carrera S's street-friendly tires and relatively compliant, daily-driver ride.

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Yes, the seatbelts are red and the carbon-fiber spoiler looks like it may have been ordered for a Honda Civic, but the C63 AMG Black Series is no poseur. For an extra $43,570, AMG completely changes the on-track demeanor of the $64,005 C63 AMG coupe. Wider tires, broader shoulders and hips, massive vents, a front splitter, jaw-mounted canards, larger brakes, a completely recalibrated suspension, and 510 horsepower combine to chop 8.5 seconds off the standard C63's lap time and match the VIR time of the SLS AMG.

Without sacrificing extravagances such as a glass roof and the usual raft of luxury equipment, AMG has dialed up feedback and grip to make the C63 feel much wieldier than its 4044 pounds might suggest. Quick steering warns of imminent slip, a solid brake pedal scrubs off speed over and over again with no change in feel. "Trust me," says the Black Series as it pounds into the uphill esses at 132.3 mph. The front tires bite into the off-camber left of sector four at 75.3 mph, 2.2 mph faster than the Ferrari 458.

We gave up on trying to time upshifts with the car in manual mode. Fail to get the upshift perfect, and the heavy-handed rev limiter shuts down power for what feels like an eternity. We opted for sport-plus mode. That mode obeys downshift requests and upshifts happen right at the redline without any need for driver intervention.

Great track cars seem to read your mind, anticipate commands, and speak affirmations. By that measure—and by its lap time—the Black Series is a great track car.